Polyurethane and polyisocyanurate foams are manufactured by reacting and foaming a mixture of ingredients comprising in general an organic isocyanate, such as pure or crude toluene diisocyanate or a polymeric diisocyanate, with an appropriate amount of polyol or mixture of polyols, in the presence of a volatile liquid blowing agent, which vaporizes during the reaction, causing the polymerizing mixture of foam. The reactivity of these ingredients is enhanced through the use of various additives such as amine and/or tin catalysts and surfactant materials which serve to control and adjust cell size as well as to stabilize the foam structure during its formation.
Flexible polyurethane foams are generally manufactured using an excess of diisocyanate which reacts with the water also included as a raw material, producing gaseous carbon dioxide, causing foam expansion. Flexible foams are widely used as cushioning materials in items such as furniture, bedding and automobiles. Auxiliary physical blowing agents such as methylene chloride and/or CFC-11 are required in addition to the water/diisocyanate blowing mechanism in order to produce low density, soft grades of flexible polyurethane foam.
Rigid polyurethane and polyisocyanurate foams are almost exclusively expanded using CFC-11 as the blowing agent. Some rigid foam formulations do incorporate small amounts of water in addition to the CFC-11, but the CFC-11 is the major blowing agent component. Other formulations sometimes use small amounts of the more volatile dichlorodifluoromethane (CFC-12) in addition to CFC-11 for producing so-called froth-type foams. Rigid foams are closed-cell foams in which the CFC-11 vapor is trapped in the matrix of cells. These foams offer excellent thermal insulation characteristics, due in part to the low vapor thermal conductivity of CFC-11, and are used widely in thermal insulation applications such as roofing systems, building panels, refrigerators and freezers and the like.
The fully halogenated chlorofluorocarbons such as CFC-11 are suspected of causing environmental problems in connection with the earth's protective ozone layer. Concern over the potential environmental impact of CFC emissions has prompted a phased reduction in fully halogenated CFC production and consumption. The azeotrope-like blowing agent blends described in this invention offer the potential of a 34 percent reduction in CFC-11 use. The other components of the blends, namely dichlorotrifluoroethane and isopentane, have very low ozone depletion potentials in comparison to CFC-11.
Although methylene chloride is used as an auxiliary blowing agent in flexible polyurethane foam manufacture, it has found very little application as a blowing agent in the rigid urethane-type foams. Methylene chloride tends to remain dissolved in the polymeric back bone of the foam due to its greater solvency characteristics. The residual methylene chloride softens and plasticizes the polymer leading to foam collapse or excessive shrinkage as well as a reduction in the strength properties of the rigid foam. Some rigid foam formulations can tolerate small amounts of methylene chloride as a component of the blowing agent, for example, Taub and Ostrozynski in U.S. Pat. No. 4,055,521 demonstrate that a blend consisting of 83 parts CFC-11, 12 parts isopentane and 5 parts methylene chloride can be used to expand a rigid polyurethane foam with good properties. However, use of even these small amounts of methylene chloride in closed-cell foams may be objectionable due to the adverse toxicological properties of methylene chloride.
Other volatile liquids such as hydrocarbons have not found acceptance as blowing agents for polyurethane-type foams due to their extreme flammability and poor thermal conductivity properties. These aspects outweigh the economic advantages that hydrocarbons have over fluorocarbons. Although the blends described in this invention do contain a hydrocarbon, it is present as a minor component and overall the blends are nonflammable as evidenced by flash point tests. Furthermore, as the present blends are azeotrope-like in nature, their vapor and liquid compositions are identical and the flammable hydrocarbon component will not fractionate or segregate from the mixture during boiling or evaporation.
U.S. Pat. Nos. 3,940,342 and 4,002,573 discloses binary constant boiling compositions of 1,2-dichloro-1,1,2-trifluoroethane with trichlorofluoromethane, with diethyl ether and with dichloromethane and also ternary constant boiling compositions comprising 1,2-dichloro-1,1,2-trichloroethane, diethyl ether and 1,2-dibromo-1,1,2,2-tetrafluoroethane.
U.S. Pat. No. 4,624,970 discloses the use of mixtures of CFC-11 and HCFC-123 or HCFC-123a to blow urethane type foams. Such blowing agent mixtures were found to permit greater amounts of low cost aromatic polyester polyols to be used in rigid foam formulations without serious degredation in foam properties.
It is accordingly an object of this invention to provide novel azeotrope-like compositions based on a fluorocarbon which is not fully halogenated, which can be used as blowing agents to produce rigid and flexible polyurethane foams and polyisocyanurate foams with good properties.
Other objects and advantages of the invention will become apparent from the following description of the invention.
In accordance with the invention, novel azeotrope-like compositions are provided comprising trichlorofluoromethane, a dichlorotrifluoroethane selected from the group consisting of 2,2-dichloro-1,1,1-trifluoroethane ethane (HCFC-123) and 1,2-dichloro-1,1,2-trifluoroethane (HCFC-123a) and isopentane which are useful as blowing agents in the manufacture of rigid and flexible polyurethane foams as well as polyisocyanurate foams. Such azeotropic compositions are formed when either of the above recited isomers of dichlorotrifluoroethane is employed in about the same proportions.
In a preferred embodiment of the invention, azeotrope-like compositions comprise from about 66 to about 80 weight percent trichlorofluoromethane (CFC-11), from about 17 to 15 weight percent of the recited dichlorotrifluoroethane isomers and from about 17 to 5 weight percent isopentane. The dichlorotrifluoroethane isomers, not being perhalogenated, are considered to be stratospherically safe. Both of the recited isomers form azeotrope-like compositions with trichlorofluoromethane and isopentane. Our best estimate of the minimum boiling azeotropic composition is about 79 weight percent CFC-11, about 15 weight percent of the recited dichlorofluoroethane isomers and about 6 weight percent isopentane. These mixtures are nonflammable liquids, do not fractionate upon evaporation or boiling and provide about 20 to 34 percent reduction in the amount of fully halogenated CFC-11 required to expand the foam. Their expansion efficiency (gas volume generated per unit weight) is better than CFC-11 alone and they also produce foams with similar thermal insulation characteristics to foams expanded with CFC-11.